/*
 *  Created on: 13/02/2018
 *      Author: ricab
 *
 * See README.md for documentation of this header's public interface.
 */

#ifndef SCOPE_GUARD_HPP_
#define SCOPE_GUARD_HPP_

#include <type_traits>
#include <utility>

#if __cplusplus >= 201703L && defined(SG_REQUIRE_NOEXCEPT_IN_CPP17)
#define SG_REQUIRE_NOEXCEPT
#endif

namespace sg {
namespace detail {
/* --- Some custom type traits --- */

// Type trait determining whether a type is callable with no arguments
template <typename T, typename = void> struct is_noarg_callable_t : public std::false_type {};  // in general, false

template <typename T>
struct is_noarg_callable_t<T, decltype(std::declval<T&&>()())> : public std::true_type {
};  // only true when call expression valid

// Type trait determining whether a no-argument callable returns void
template <typename T> struct returns_void_t : public std::is_same<void, decltype(std::declval<T&&>()())> {};

/* Type trait determining whether a no-arg callable is nothrow invocable if
required. This is where SG_REQUIRE_NOEXCEPT logic is encapsulated. */
template <typename T>
struct is_nothrow_invocable_if_required_t : public
#ifdef SG_REQUIRE_NOEXCEPT
                                            std::is_nothrow_invocable<T> /* Note: _r variants not enough to
                                                                            confirm void return: any return can be
                                                                            discarded so all returns are
                                                                            compatible with void */
#else
                                            std::true_type
#endif
{
};

// logic AND of two or more type traits
template <typename A, typename B, typename... C>
struct and_t : public and_t<A, and_t<B, C...>> {};  // for more than two arguments

template <typename A, typename B>
struct and_t<A, B> : public std::conditional<A::value, B, A>::type {};  // for two arguments

// Type trait determining whether a type is a proper scope_guard callback.
template <typename T>
struct is_proper_sg_callback_t : public and_t<is_noarg_callable_t<T>, returns_void_t<T>,
                                              is_nothrow_invocable_if_required_t<T>, std::is_nothrow_destructible<T>> {
};

/* --- The actual scope_guard template --- */

template <typename Callback, typename = typename std::enable_if<is_proper_sg_callback_t<Callback>::value>::type>
class scope_guard;

/* --- Now the friend maker --- */

template <typename Callback>
detail::scope_guard<Callback> make_scope_guard(Callback&& callback) noexcept(
    std::is_nothrow_constructible<Callback, Callback&&>::value); /*
we need this in the inner namespace due to MSVC bugs preventing
sg::detail::scope_guard from befriending a sg::make_scope_guard
template instance in the parent namespace (see https://is.gd/xFfFhE). */

/* --- The template specialization that actually defines the class --- */

template <typename Callback> class scope_guard<Callback> final {
   public:
    typedef Callback callback_type;

    scope_guard(scope_guard&& other) noexcept(std::is_nothrow_constructible<Callback, Callback&&>::value);

    ~scope_guard() noexcept;  // highlight noexcept dtor

    void dismiss() noexcept;

   public:
    scope_guard() = delete;
    scope_guard(const scope_guard&) = delete;
    scope_guard& operator=(const scope_guard&) = delete;
    scope_guard& operator=(scope_guard&&) = delete;

   private:
    explicit scope_guard(Callback&& callback) noexcept(std::is_nothrow_constructible<Callback, Callback&&>::value); /*
                                                                                              meant for friends only */

    friend scope_guard<Callback> make_scope_guard<Callback>(Callback&&) noexcept(
        std::is_nothrow_constructible<Callback, Callback&&>::value); /*
only make_scope_guard can create scope_guards from scratch (i.e. non-move)
*/

   private:
    Callback m_callback;
    bool m_active;
};

}  // namespace detail

/* --- Now the single public maker function --- */

using detail::make_scope_guard;  // see comment on declaration above

}  // namespace sg

////////////////////////////////////////////////////////////////////////////////
template <typename Callback>
sg::detail::scope_guard<Callback>::scope_guard(Callback&& callback) noexcept(
    std::is_nothrow_constructible<Callback, Callback&&>::value)
    : m_callback(std::forward<Callback>(callback)) /* use () instead of {} because
      of DR 1467 (https://is.gd/WHmWuo), which still impacts older compilers
      (e.g. GCC 4.x and clang <=3.6, see https://godbolt.org/g/TE9tPJ and
      https://is.gd/Tsmh8G) */
      ,
      m_active{true} {}

////////////////////////////////////////////////////////////////////////////////
template <typename Callback> sg::detail::scope_guard<Callback>::~scope_guard<Callback>() noexcept {
    if (m_active) m_callback();
}

////////////////////////////////////////////////////////////////////////////////
template <typename Callback>
sg::detail::scope_guard<Callback>::scope_guard(scope_guard&& other) noexcept(
    std::is_nothrow_constructible<Callback, Callback&&>::value)
    : m_callback(std::forward<Callback>(other.m_callback))  // idem
      ,
      m_active{std::move(other.m_active)} {
    other.m_active = false;
}

////////////////////////////////////////////////////////////////////////////////
template <typename Callback> inline void sg::detail::scope_guard<Callback>::dismiss() noexcept { m_active = false; }

////////////////////////////////////////////////////////////////////////////////
template <typename Callback>
inline auto sg::detail::make_scope_guard(Callback&& callback) noexcept(
    std::is_nothrow_constructible<Callback, Callback&&>::value) -> detail::scope_guard<Callback> {
    return detail::scope_guard<Callback>{std::forward<Callback>(callback)};
}

#endif /* SCOPE_GUARD_HPP_ */
